The invention relates to an integrated particle counter-mass spectrometer system, and, more particularly, to a mechanism for collecting particles from a particle counter and delivering the collected particles to a mass spectrometer.
Microcontamination is an ongoing problem in a modern semiconductor facility. Line widths are approaching 0.16 microns in diameter, and commercially fatal defects are quickly approaching 0.05 microns in diameter. Advancements in semiconductor manufacture serve to exacerbate the contamination problems.
Commercially fatal defects are produced by human exfoliation of particles, moving parts in machines, and even the robots used to move wafers from cassettes to tools. Thus, a clean room is under a constant barrage of defect producing commercially fatal sized particles.
Microcontamination engineers battle this problem with condensation and particle counters. This enables them to monitor the quantity of particles per volume of air and also the distribution of the size of the particles. However, these techniques fall short of meeting the challenge offered by the progressively decreasing size of semiconductor line widths.
Laser particle counters work by moving a volume of air through a laser field. The particles scatter the laser beams causing a scattering event that can be monitored and yield a measurement of the particle""s size.
Mass spectrometers use an inlet, an ion source, a mass analyzer, an ion detector, a data output from the ion detector, and a data system. The data system processes the output into a chart of abundance versus mass.
Mass spectrometry is a generalized technique whereby a mass per charge can be separated through a dynamic range. Mass spectrometry is a powerful technique that is able to analyze gases (electron impact mass spectrometry), liquids (inductively coupled plasma mass spectrometry and gas chromatography), solids (glow discharge mass spectrometry and secondary ion mass spectrometry). It is used to determine the structural identity of complex compounds, separate out phases of materials in the gaseous form, analyze the elemental composition of material, depth profile elemental concentration of one atomic species in a substrate and multiple other uses throughout the scientific disciplines. Essentially all mass spectrometers have the same basic components. A sample is introduced into the mass spectrometer and is ionized by some energy source. The ions travel though a mass analyzer where the ions are sorted and separated from one and other. Finally a detector of some sort is used to quantify the relative intensities of the different ion species.
One form of mass spectrometry is known as secondary ion mass spectrometry (SIMS). SIMS is a process whereby a primary ion beam is used to expel secondary ion from a sample su ace through the means of a collision cascade. The ejected ions are then separated by mass to analytically characterize the properties of a surface region of a solid. SIMS is mainly used today to analyze small quantities of elements in impurity analysis. By focusing the primary ion beam through a series of electromagnetic lenses and then rastering it in a specific pattern, the primary ion beam will begin to sputter away the sample surface. This is know as dynamic SIMS. Through a monitoring of the expelled secondary ions, a depth profile of composition and concentration versus depth can be produced. The resultant profile can be made to quantify the distribution of elements at and below a sample surface.
SIMS uses an ion probe and also detects an ion species. Similar to RBS (Rutherford Backscattering Spectroscopy), SIMS has an ability to analyze all of the elements of the periodic table. By way of contrast, EDX (Energy Dispersive X-ray Spectroscopy), XPS (X-ray Photoelectron Spectroscopy), and AES (Auger Electron Spectroscopy) have limited abilities in conjunction with lighter elements. The biggest advantage over similar surface analysis techniques comes from SIMS detection lower limit and vast dynamic range. SIMS can measure all elements down to the part per million range and some down to detection limits of a part per billion. This is considerably beyond the detection limits of AES, XPS, EDX, which is in the range of 0.1 to 1 ppm, and RPS which is around 100 ppm.
The most common prima ion beams for SIMS are O2+ for electropositive elements and Cs+ for electronegative elements. Other primary beam ions are used for specific types of applications but cesium and oxygen ions are the two most commonly used. A primary ion beam is directed to impact a sample surface, causing a scattering of material belonging both to the sample surface and the primary ion beam. The secondary ions emitted from the sample can carry a wide variety of energy from a few eV to energies approaching the incident beam energy. As the primary beam impacts the sample surface, a transfer of energy occurs between the incident primary ion and the atoms on the surface of the ample. The collision cascade is the closest model to describe the movements of the primary ion beam as it interacts with the atoms of the sample. The collision cascade describes the transfer of energy from the incident ions to target atoms that then continue to transfer the energy through collisions to other surrounding atoms until the energy is equilibrated with the sample surface. The primary ions can penetrate to a depth Rp, the penetration depth below the sample surface. Collisions that occur near or at the surface that eject ion into the vacuum of the system, result in the formation of what is called secondary ion and it is these that are analyzed by the mass spectrometer. The effect of this sputtering can lead to surface morphology roughness due to lattice plane locations. The effect can be minimized by rotation of the sample during sputtering.
The present invention relates to a device for testing particles for composition and concentration. The device includes a particle counter, a collector screen, and a mass spectrometer. In one embodiment, the collector screen is positioned to receive particles received by the particle counter, and the mass spectrometer is positioned to receive counted particles retained on the collector screen.